Retroreflective products have been widely used in signs as road sign and engineering sign, license plates for vehicles as automobile or motorcycle, safety materials as clothes and life-saving appliances and marks as advertising board, etc. The retroreflective products have been developed currently comprise those of bead and prism types (such as cubic angle). These products can guaranty safety in some harsh environments. For example, when used in the environments with extreme temperature conditions, low visibility, atmospheric pollution, or photochemical reactions caused by infrared, visible, ultraviolet radiations in sunlight, the retroreflective products can be recognized easily.
The retroreflective products are most widely used in vehicle license plates. Normally, the retroreflective sheeting with adhesives should be firstly pasted onto a base material as aluminum alloy plate; as the marking part is printed through the methods as roller painting or hot stamping after being molded by a convex pattern, a license plate is then manufactured.
As for the retroreflective sheeting disclosed in the patent literature EP1225554A1 by Petra et al., the actual elongation of which when ruptured is more than 40%, but vinyl chloride resin is used in the disclosed embodiments. Such retroreflective sheeting is soft and can meet the processing requirements, but the resins as vinyl chloride resin and polyurethane resin have poor weatherability and durability. As the license plates as vehicle license plate, road sign and engineering sign should be used in the open air for a long time, they must have outstanding weatherability, therefore, such resins are not suitable for the signs as road sign and engineering sign, or the license plates for vehicles as automobile or motorcycle that need durability.
In addition, Nakazawa Hiroki et al. have disclosed a retroreflective sheeting in the patent literature CN200680004431.9, which uses acrylic resin, alkyd resin and polyester resin, butyral resin for its surface and mentioned that these resins are in favor of improving the weatherability of the retroreflective sheeting. Meanwhile, they also mentioned in the Embodiments that the used acrylic resin is a copolymer of three resins as butyl acrylate resin, methyl methacrylate resin and acrylic acid resin; however, neither real improvement nor contrastive analysis on the improvement of weatherability is specified therein. Moreover, although acrylic resin is helpful to improve the weatherability of the retroreflective sheeting, it has high hardness and poor softness. Therefore, the retroreflective sheeting might be ruptured during convex pattern molding when a license plate is manufactured, thus the resin is hard to be used for producing license plates.
Therefore, a retroreflective sheeting that can meet the requirements for both weatherability and processing and the methods for manufacturing the retroreflective sheeting and the vehicle license plate adopting such retroreflective sheeting are desperately in need.